Yield of plants

ABSTRACT

Exogenous use of betaine on tobacco plants improves the yield, especially tobacco plants grown under stress conditions.

This application is a 371 of PCT/FI95/00482 filed Sep. 7, 1995.

TECHNICAL FIELD

The invention relates to the use of betaine to improve the yield ofplants. The invention relates especially to the use of betaine toimprove the yield of tobacco plants (Nicotiana spp. ). According to theinvention, the yield can be improved particularly under stressconditions, i.e. when the conditions are poor due to e.g. drought, highsalinity, low temperatures, a humidity or environmental poisonsinterfering with the growth. The invention also relates to tobaccoplants treated with betaine, to tobacco leaves and other parts of atobacco plant, and to products prepared from these.

BACKGROUND

The environment and conditions of growth considerably affect the yieldof plants. Optimum growth environment and conditions usually result in ayield that is large in quantity and high in quality. Under poor growthconditions both the quality and the quantity naturally deteriorate.

The physiological properties of a plant are manipulated by means ofbreeding, both with traditional breeding methods and for example withgenetic manipulation.

Several different solutions concerning cultivation technique have beendeveloped to improve the growth conditions and yield of plants.Selecting the right plant for the right growth location is self-evidentfor a person skilled in the art. During the growing season plants may beprotected with mechanical means by utilizing for example differentgauzes or plastics or by cultivating the plants in greenhouses.Irrigation and fertilizers are generally used in order to improve thegrowth. Surfactants are often used in connection with applyingpesticides, protective agents and minerals. Surfactants improve thepenetration of substances to plant cells, thereby enhancing andincreasing the effect of the aforementioned agents and simultaneouslyreducing their harmful effects on the environment. However, differentmethods of cultivation technique are often laborious and impractical,their effect is limited (the economical size of a greenhouse, thelimited protection provided by gauzes, etc.), and they are also far tooexpensive on a global scale. No economically acceptable chemicalsolutions for protecting plants from environmental stress conditionshave been described so far.

Water supply is more important than any other environmental factor forthe productivity of a crop. Irrigation is usually utilized to ensuresufficient water supply. However, there are significant health andenvironmental problems related to irrigation, for example a sharpdecrease in water resources, deterioration of water quality anddeterioration of agricultural lands. It has been calculated in the fieldthat about half of the artificially irrigated lands of the world aredamaged by waterlogging and salinization. An indication of thesignificance and scope of the problem is that there are 255 millionhectares of irrigated land in the world, and they account for 70% of thetotal world water consumption. In the United States alone, there areover 20 million hectares of irrigated land mainly in the area of the 18western states and in the southeastern part of the country. They use 83%of the total water consumption for irrigation alone. It can also benoted that the use of irrigation water increases every year especiallyin industrial countries. In addition to these problems, another drawbackof irrigation is the high cost.

The productivity of plants in dry conditions, i.e. the sensitivity ofcrops to drought, varies according to the plant variety. Crop species,such as tobacco (Nicotiana spp.), that produce fresh leaves are highlysensitive to drought, and they cannot be produced commercially in areasor during seasons with a limited water supply and a high degree ofevaporation.

Another serious stress factor is the salinity of soil. The salinity ofsoil can be defined in different ways; according to the generaldefinition, soil is saline if it contains soluble salts in an amountsufficient to interfere with the. growth and yield of several cultivatedplant species. The most common of the salts is sodium chloride, butother salts also occur in varying combinations depending on the originof the saline water and on the solubility of the salts.

It is difficult for plants growing in saline soil to obtain a sufficientamount of water from the soil having a negative osmotic potential. Highconcentrations of sodium and chloride ions are poisonous to plants. Anadditional problem is the lack of minerals, which occurs when sodiumions compete with potassium ions required, however, for cell growth,osmoregulation and pH stabilization. This problem occurs especially whenthe calcium ion concentration is low.

The productivity of plants and their sensitivity to the salinity of soilalso depend on the plant species. Halophytes require relatively highsodium chloride contents to ensure optimum growth, whereas glycophyteshave low salt tolerance or their growth is considerably inhibitedalready at low salt concentrations. There are great differences evenbetween different cultivars of a cultivated plant species. The salttolerance of one and the same species or cultivar may also varydepending for example on the stage of growth. In the case of low ormoderate salinity, the slower growth of glycophytes cannot be detectedin the form of specific symptoms, such as chlorosis, but it is shown inthe stunted growth of the plants and in the colour of their leaves thatis darker than normal. Moreover, the total leaf area is reduced, carbondioxide assimilation decreases and protein synthesis is inhibited.

Plants can adapt to some extent to stress conditions. This abilityvaries considerably depending on the plant species. As a result of theaforementioned stress conditions, certain plants begin to produce agrowth hormone called abscisic acid (ABA), which helps the plants toclose their stomata, thus reducing the severity of stress. However, ABAalso has harmful side effects on the productivity of plants. ABA causesfor example leaf, flower and young fruit drop and inhibits the formationof new leaves, which naturally leads to reduction in yield.

Stress conditions and especially lack of water have also been found tolead to a sharp decrease in the activity of certain enzymes, such asnitrate reductase and phenylalanine ammonium lyase. On the other hand,the activity of alpha-amylase and ribonuclease increases. No chemicalsolutions, based on these findings, to protect plants have beendescribed so far.

It has also been found that under stress conditions certain nitrogencompounds and amino acids, such as proline and betaine, are accumulatedin the regions of growth of certain plants. The literature of the artdiscusses the function and meaning of these accumulated products. On theone hand it has been proposed that the products are by-products ofstress and thus harmful to the cells, on the other hand it has beenestimated that they may protect the cells (Wyn Jones, R. G. and Storey,R.: The Physiology and Biochemistry of Drought Resistance in Plants,Paleg, L. G. and Aspinall, D. (Eds.), Academic Press, Sydney, Australia,1981).

Zhao et al. (in J. Plant Physiol. 140 (1992) 541-543) describe theeffect of betaine on the cell membranes of alfalfa. Alfalfa seedlingswere sprayed with 0.2M glycinebetaine, whereafter the seedlings wereuprooted from the substrate, washed free of soil and exposed totemperatures from -10° C. to -2° C. for one hour. The seedlings werethen thawed and planted in moist sand for one week at which timeregrowth was apparent on those plants that had survived. Glycinebetaineclearly improved the cold stability of alfalfa. The effect wasparticularly apparent at -6° C. for the cold treatment. All controlsheld at -6° C. for one hour died, whereas 67% of the seedlings treatedwith glycinebetaine survived.

Itai and Paleg (in Plant Science Letters 25 (1982) 329-335) describe theeffect of proline and betaine on the recovery of water-stressed barleyand cucumber. The plants were grown in washed sand, and polyethyleneglycol (PEG, 4000 mol. wt.) was added to the nutrient solution for fourdays in order to produce water stress, whereafter the plants wereallowed to recover for four days before harvesting. Proline and/orbetaine (25 mM, pH 6.2) was sprayed on the leaves of the plant either onthe first or third day of the stress or immediately before harvesting.As regards barley, it was noted that betaine supplied either before orafter the stress had no effect, whereas betaine added in the end of thestress was effective. Proline had no effect. No positive effect wasapparent for cucumber. On the contrary, it was found out that bothbetaine and proline had a negative effect.

Experiments aiming at clarifying the effects of betaine and proline onplants have thus yielded contradictory results, and there are nocommercial applications based on these results.

BRIEF DESCRIPTION OF THE INVENTION

The purpose of the present invention was to find a way to partiallyreplace artificial irrigation so that the amount and quality of theyield could be simultaneously ensured. Another purpose of the inventionwas to find a way to protect plants also under other stress conditions,such as during high salinity often connected with drought, at lowtemperatures, etc. Moreover, a further aim was to find a way to increasethe yield under normal conditions without utilizing methods that wouldconsume environmental resources or harm the environment.

In connection with the present invention it has now surprisingly beenfound that the yield of tobacco plants, for example the amount andquality of the yield, can be considerably improved by means of betainethat is applied exogenously. Betaine has been found to be especiallyeffective in improving the yield under stress conditions, and it has nosuch detrimental effects as the side effects of ABA.

The invention thus relates to the exogenous use of betaine to improvethe yield of tobacco plants. According to the invention, betaine is usedexogenously to improve the yield of plants under both normal and stressconditions.

The invention also relates to tobacco leaves of tobacco plants treatedexogenously with betaine, and to the use of the leaves in products oftobacco industry.

The invention also relates to a method of improving the yield of tobaccoplants, in which method betaine is exogenously applied to growingtobacco plants.

Betaine is applied to the plant in either one or several successivetreatments. The application may be performed for example by sprayingtogether with for example a fertilizer, if desired. Betaine usedaccording to. the invention is transported to plant cells, where itactively regulates the osmotic balance of the cells and alsoparticipates in other processes of cell metabolism. A plant cell treatedwith betaine is more viable even when subjected to exogenous stressfactors.

The betaine treatment according to the invention is economicallyadvantageous, and the yield increases in an amount that is economicallyprofitable and significant. The treatment does not produce significantlymore work since it may be performed together with other sprayings, andit does not require new investments in machinery, equipment or space. Itshould also be noted that betaine is a non-toxic natural product, whichhas no detrimental effects on the quality of the yield. Betaine is alsoa stable substance that remains in the plant cells and thereby has along-standing effect.

DETAILED DESCRIPTION OF THE INVENTION

Betaine refers to fully N-methylated amino acids. Betaines are naturalproducts that have an important function in the metabolism of bothplants and animals. One of the most common betaines is a glycinederivative wherein three methyl groups are attached to the nitrogen atomof the glycine molecule. This betaine compound is usually calledbetaine, glycinebetaine or trimethylglycine, and its structural formulais presented below: ##STR1##

Other betaines are for example alaninebetaine and prolinebetaine, whichhas been reported to for example prevent perosis in chicks. R. G. WynJones and R. Storey describe betaines in detail in The Physiology andBiochemistry of Drought Resistance in Plants (Paleg, L. G. and Aspinall,D. (Eds.), Academic Press, Sydney, Australia, 1981). The reference isincluded herein by reference.

Betaine has a bipolar structure and it contains several chemicallyreactive methyl groups which it can donate in enzyme-catalyzedreactions. Most organisms can synthesize small amounts of betaine forexample for the methyl function, but they cannot react to stress bysubstantially increasing the production and storage of betaine. Bestknown organisms accumulating betaine are plants belonging to theChenopodiaceae family, for example sugar beet, and some microbes andmarine invertebrates. The main reason for the betaine accumulation inthese organisms is probably that betaine acts as an osmolyte and thusprotects the cells from the effects of osmotic stress. One of the mainfunctions of betaine in these plants and microbes is to increase theosmotic strength of the cells when the conditions require this, forexample in case of high salinity or drought, thus preventing water loss.Unlike many salts, betaine is highly compatible with enzymes, and thebetaine content in cells and cell organelles may therefore be highwithout having any detrimental effect on the metabolism. Betaine hasalso been found to have a stabilizing effect on the operation ofmacromolecules; it improves the heat resistance and ionic tolerance ofenzymes and cell membranes. Tobacco plants do not normally store betainein their cells.

Betaine can be recovered for example from sugar beet withchromatographic methods. Betaine is commercially available from CultorOy, Finnsugar Bioproducts as a product that is crystalline water-freebetaine. Other betaine products, such as betaine monohydrate, betainehydrochloride and raw betaine liquids, are also commercially availableand they can be used for the purposes of the present invention.

According to the present invention, betaine is thus used exogenously toimprove the yield of tobacco plants. According to the invention, betaineis used to improve the yield of tobacco plants especially under stressconditions, i.e. when the plants are subjected to periodic or continuousexogenous stress. Such exogenous stress factors include for exampledrought, high temperatures, high salinity, herbicides, environmentalpoisons, etc. Treating plants subjected to stress conditions exogenouslywith betaine for example improves the adaptation of the plants to theconditions and maintains their growth potential longer, therebyimproving the yield-producing capacity of the plants. Betaine is also astable substance that remains in the plant cells. The positive effect ofbetaine is thereby long-standing and diminishes only gradually due todilution caused by the growth.

Even though this reference and the claims use the word `betaine`, it isclear that according to the invention several different betaines can beused. It should also be noted that betaine is used here as a generalterm which thus covers different known betaines.

Betaine is applied to tobacco plants in either one or several successivetreatments. Application in a single dose is considered preferable. Theamount used varies depending on the tobacco cultivar and the stage ofgrowth. A useful amount may be for example about 0.2 to 40 kg of betaineper hectare. A preferable amount is thus for example about 3 to 9 kg ofbetaine per hectare. The amounts given here are only suggestive; thescope of the present invention thus contains all amounts that work inthe manner described herein.

Any method suitable for the purpose may be used to apply betaine.Betaine can be applied separately or together with other plantprotectants, pesticides or nutrients, such as fungicides and urea ormicronutrients. Betaine can be applied easily for example by spraying.Foliar application of betaine and possible other agents through sprayingis a preferable method which enables a more rapid response than methodsinvolving root application. However, there may be different problemsrelated to this method, such as low penetration concentrations in leaveswith thick cuticles, run-off from hydrophobic surfaces, washing off byrain, rapid drying of the solution and leaf damage. In order to avoidthese problems it is worthwhile to consider using also other methods toapply betaine.

According to the invention, betaine is preferably used in the form of anaqueous solution.

The time of the treatment according to the invention may also vary. Ifbetaine is applied in a single treatment, the treatment is usuallyperformed at an early stage of growth, for example when the leaves havejust come out. If betaine is applied in several successive treatments, anew spraying is performed preferably in the beginning of flowering orwhen stress can be forecasted on the basis of the weather.

The betaine treatment according to the invention considerably improvesthe yield of tobacco plants, for example the amount and quality of theyield. The treatment according to the invention is economicallyadvantageous and the increase in the yield is economically profitableand significant. The invention has shown that the tobacco yield can beincreased by over 30% with a suitable betaine dosage, for example about2 to 7 kg/ha. It should also be noted that even though the amount ofyield increases to a considerable extent, the quality does notdeteriorate. On the contrary, it has been proved here that the increasein the yield results from both a greater fresh weight and surface of theleaves, and from an earlier and more even maturation of the leaves.

According to the invention, the tobacco yield can be improved both undernormal and stress conditions, which in addition to drought include forexample a high salinity often connected with drought, a hightemperature, etc. It should also be noted that the present inventionalso makes it possible to cultivate tobacco plants in areas that werepreviously considered unfit for cultivation, thus allowing fertile landsto be used for the cultivation of traditional nutrients, such as potato,grain, beans, etc.

The invention will be described in greater detail by means of thefollowing examples. The examples are only provided to illustrate theinvention, and they should not be considered to limit the scope of theinvention in any way.

EXAMPLE 1

Two experiments were conducted during the spring and summer in order todetermine the effects of different betaine concentrations on tobacco.

The experiments were conducted in the spring in Finland (60° 13' N, 24°57' E) in the greenhouses of the University of Helsinki by utilizing theCompletely Randomised Design. Forty-eight pots with a plant in each wereinvolved in the experiment. The experiment was repeated in the summermonths using the same plant material and methods as in the firstexperiment. The only deviation was the inducement of water stress in thesecond experiment three weeks earlier than in the first. Five-week oldtobacco (Nicotiana tabacum, cv. Samsung) seedlings were transplantedinto black, bottom-perforated plastic pots (475 ml, .O slashed. 11 cm)containing vermiculite and peat in the ratio of 1:1 by volume. The potswere watered adequately until the plants were 12 weeks old, 48 cm inheight and had a mean leaf number of 17. They were then subjected towater stress corresponding to a pF value of 2.9, which corresponds toabout 36% soil moisture by weight in the soil medium and themeterological conditions of the greenhouse, the water stress beinginduced by applying 17 ml of water every 24 hours. The plants were thentopped by removing the terminal buds in order to stimulate leafexpansion. Visual symptoms of leaf droop were correlated to the desiredpF of 2.9 and used as the index for maintaining the status.

A fertilizer formulation of NPK 6:4:6 (Kemira Oy, Vaasa, Finland) wasadministered biweekly two weeks after the transplanting at the rate of50 kg/ha until the imposition of the treatments. Insect pests werecontrolled with Bladafum II (Bayer) containing 11.6% of sodium chlorateas the active ingredient. Photoperiod was adjusted to 17 hours with fournatrium lamps (400 W, AIRAM, Oy Airam Ab, Finland), providing a meanmaximum daylight temperature of 28° C. and photosynthetically activeradiation (PAR) of 434 μmol m² /s. The mean night temperature was 12° C.and the relative humidity fluctuated between 42 and 45%.

A day after the water stress was induced, the plants were treated withbetaine (Finnsugar Bioproducts, Finland). Two different betaine contentswere used: 0.1M betaine aqueous solution (L) and 0.3M betaine aqueoussolution (H). An aqueous solution (C) was control. Each plant received20 ml of solution, with both the top and underneath of the leavesthoroughly wetted using a manually operated atomizer.

The total number of leaves per plant was recorded at harvest and theleaves were divided into green (>80% of the leaves were green) andyellow. The total leaf area (dm²) per plant was also determined atharvest using a portable LI-COR planimeter (Model LI-3000, LI-COR Inc.,Lincoln, Nebr., USA). The area of both green and yellow leaves wasmeasured.

The fresh weight and the dry weight of the leaves were determined 16days after the betaine treatment, whereupon the leaves were detachedfrom the stem and the fresh weight was recorded by weighing (g/plant).The leaves were then dried at 50° C. for 20 hours, cooled indesiccators, and the dry weight (g/plant) and dry matter content werecalculated.

The betaine content of the plants was determined 24 hours, and 4, 10 and16 days (harvest) after the betaine application in the following manner.The five uppermost leaves were detached and washed in cold running waterto dissolve and remove all adhering betaine crystals. The leaves werethen dried, pulverized in liquid nitrogen, placed into cryotubes andstored in vacuum tanks containing liquid nitrogen (-196° C.) until thebetaine content was determined with a HPLC method Rajakyla andPaloposki, J. Chromatography 282 (1983) 595-602!

The results were analyzed statistically by means of variance analysisusing the MSTAT-C program.

The fresh weight of tobacco plants increased in both experiments due tothe betaine application. There was an increase of 10% in the freshweight in Experiment I with the 0.1M betaine solution (L), whereas inExperiment II the same treatment produced a 30% increase in the freshweight as compared with the control (C). The application of 0.3M betainesolution (H) provided 13% and 20% increases in the fresh weight over thecontrol in Experiments I and II, respectively (p<0.05). The results areshown in Table 1.

                  TABLE 1                                                         ______________________________________                                        Effect of betaine on the fresh weight of water-                               stressed tobacco leaves                                                                             Mean fresh  % of the                                    Experiment                                                                              Treatment*  weight (g/plant)                                                                          control                                     ______________________________________                                        I         C           68.3        100                                                   L           75.4        110                                                   H           76.9        113                                         II        C           38.9        100                                                   L           50.3        130                                                   H           46.6        120                                         ______________________________________                                         *C = control                                                                  L = 0.1M betaine                                                              H = 0.3M betaine                                                              LSD = 3.70 at level 0.05                                                 

The significant difference between the two experiments in the freshweight of the leaves resulted from the timing of the experiments.Experiment I was terminated 10 weeks after transplanting, when the totalage of the plants was 15 weeks. Experiment II in turn was terminated 5weeks earlier, since the water stress was imposed to coincide with thestage of rapid growth. The effects of the betaine treatment were alsothe greatest then.

The dry weight of tobacco leaves also increased in both experiments dueto the betaine application. In Experiment I there was an increase of 8%in the dry weight with 0.1M betaine solution (L), whereas the sametreatment in Experiment II produced a 32% increase in the dry weightover the control. Using the 0.3M betaine solution (H) produced 16 and25% increases in the dry weight over the control in Experiments I and IIrespectively. The differences in these experiments were also due to thetiming of the experiments. The results are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Effect of betaine on the dry weight of water-                                 stressed tobacco leaves                                                                             Mean dry    % of the                                    Experiment                                                                              Treatment*  weight (g/plant)                                                                          control                                     ______________________________________                                        I         C           11.3        100                                                   L           12.2        108                                                   H           13.1        116                                         II        C           6.8         100                                                   L           9.0         132                                                   H           8.5         125                                         ______________________________________                                         *C = control                                                                  L = 0.1M betaine                                                              H = 0.3M betaine                                                              LSD = 0.59 at level 0.05                                                 

There were increases of 14% and 12% in the total leaf area in ExperimentI over the control with treatments L and H, whereas the same treatmentsin Experiment II produced 35% and 26% increases over the control. Theresults are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                        Effect of betaine on the total leaf area of                                   water-stressed tobacco leaves                                                                        Mean leaf                                                                              % of the                                      Experiment                                                                              Treatment*   area (dm.sup.2)                                                                        control                                       ______________________________________                                        I         C            34.4     100                                                     L            39.1     114                                                     H            38.6     112                                           II        C            6.9      100                                                     L            9.3      135                                                     H            8.7      126                                           ______________________________________                                         *C = control                                                                  L = 0.1M betaine                                                              H = 0.3M betaine                                                              LSD = 0.76 at level 0.05                                                 

The number of green leaves in water-stressed tobacco plants at harvestdecreased as a result of the betaine application. In Experiment I, therewere 3% and 5% decreases in the number of green leaves at harvest due totreatments L and H, respectively. In Experiment II, treatment L produceda decrease of 5% in the number of green leaves at harvest, whereastreatment H produced a decrease of 20% in the number of green leaves.The results are shown in Table 4.

                  TABLE 4                                                         ______________________________________                                        Effect of betaine on the number of green leaves                               of water-stressed tobacco plants                                                                  Mean number of green                                                                         % of the                                   Experiment                                                                             Treatment* leaves per plant                                                                             control                                    ______________________________________                                        I        C          38.25          100                                                 L          37.25          97                                                  H          35.75          95                                         II       C          20.50          100                                                 L          20.00          95                                                  H          16.25          80                                         ______________________________________                                         *C = control                                                                  L = 0.1M betaine                                                              H = 0.3M betaine                                                              LSD = 1.37 at level 0.05                                                 

A higher betaine content thus increased more the maturation of tobacco.Fast and even maturation is important since it reduces the number ofharvests, thus reducing also the total costs.

About 13% of betaine used in all the experiments was absorbed by theleaves. In Experiment I, treatments L and H provided the absorptionrates of 14% and 13%, respectively. The corresponding results inExperiment II were 12% and 11%. The proportion of absorbed betaine canbe increased with a surfactant, whereupon the amount of betaine used canbe correspondingly reduced. The absorption ratio was 0:1:3 fortreatments C, L and H, respectively, corresponding thus entirely to thebetaine concentrations used. Betaine was highly stable in the leaftissue of the plants; after 16 days over 50% of the originally absorbedbetaine was still present as determined by HPLC. The results are shownin Table 5. The decrease in the betaine content of a plant probablyresults from a dilution effect brought about by leaf expansion.

                  TABLE 5                                                         ______________________________________                                        Betaine content of water-stressed tobacco plants                                        Days after                                                                             Result of treatment, mean                                  Experi-   betaine  (% of fresh weight)                                        ment      treatment                                                                              C*          L*   H*                                        ______________________________________                                        I         1        <0.01       0.13 0.35                                                4        <0.01       0.13 0.49                                                10       <0.01       0.18 0.48                                                16       <0.01       0.17 0.47                                      II        1        <0.01       0.22 0.65                                                4        <0.01       0.21 0.59                                                10       <0.01       0.16 0.44                                                16       <0.01       0.11 0.31                                      ______________________________________                                         *C = control                                                                  L = 0.1M betaine                                                              H = 6.3M betaine                                                         

The positive effect of the exogenous betaine application on the tobaccoyield is clearly apparent from the results given above. In addition toincreasing the fresh weight and dry weight of the leaves, as well as theleaf area, the betaine application also improved the early and evenmaturration of the leaves. Betaine was also found to be stable in leaftissues, which is an indication of its ability to protect the treatedplants in the long term.

EXAMPLE 2

The experiments described in Example 1 are repeated as field experimentswith the betaine application rates of 3 kg/ha and 9 kg/ha. The fieldexperiments are conducted in traditional tobacco plantations where about50,000 plants grow per hectare. After the cultivation the tobacco leavesare gathered and weighed, and they are then dried in the air to amoisture content of about 15% and then weighed again. The yield oftobacco leaves is shown in Table 6.

                  TABLE 6                                                         ______________________________________                                        Effect of betaine on the yield of tobacco leaves                                              Fresh yield                                                                             Dry yield                                           Betaine (kg/ha) (kg/ha)   (kg/ha)                                             ______________________________________                                        0 (control)     665       565                                                 3               720       610                                                 9               770       655                                                 ______________________________________                                    

Betaine thus has a considerable effect on the yield. Utilizing a smallerdosage provides an increase of about 8% in the yield, whereas a higherdosage increases the yield as much as 16%.

We claim:
 1. A method for improving the yield of tobacco plants growingunder stress conditions, wherein an effective amount of betaine isexogenously applied to growing tobacco plants.
 2. A method according toclaim 1, wherein the stress conditions comprise high or lowtemperatures, drought, excess humidity or high salinity.
 3. A methodaccording to claim 2, wherein the plant grows under water stress.
 4. Amethod according to claim 1, wherein betaine is administered togetherwith a fertilizer or a surfactant.
 5. A method according to claim 1,wherein betaine is administered once or several times during the growingseason.
 6. A method according to claim 5, wherein betaine isadministered in a single treatment at an early stage of growth.
 7. Amethod according to claim 1, wherein betaine is used in an amount ofabour 0.2 to 40 kg/ha.
 8. A method according to claim 7, wherein betaineis used in an amount of about 3 to 9 kg/ha.